1. Field of the Invention
The present invention relates to a microwave oven, and more particularly, to a microwave oven including a rotary tray and a linearly reciprocating tray, which enable food to be uniformly cooked.
2. Description of the Related Art
Microwave ovens are cooking devices using electronic waves. A microwave oven projects microwaves to food to be cooked to vibrate water molecules in the food, and cooks the food using frictional heat generated between water molecules as heat for cooking the food.
When the microwaves are projected and reflected from the inner walls of a cooking chamber, traveling microwaves and the reflected microwaves are superposed, and the electromagnetic field formed within the microwave ovens exhibits strong and weak spots. Due to the inconsistent distribution of the electromagnetic field, food cannot be heated uniformly, so that food is imperfectly cooked. Thus, to avoid this phenomenon, food, i.e. an object to be cooked, is moved or the traveling direction of the microwaves is changed such that the microwaves are uniformly projected to the food if possible.
Among the conventional methods, the method of using a rotary tray is widely known. However, the method of using a rotary tray has disadvantages in that, when long food is placed on the rotary tray, the long food contacts the rear wall of the cooking chamber or the inner surface of a door so that the long food cannot be smoothly rotated and cooked. By taking this problem into consideration, a tray linearly reciprocating in the lateral direction is utilized. However, in comparison with the rotary tray, the linearly reciprocating tray has a limited ability to uniformly cook food.
Recently, a tray assembly using the rotary tray and the linearly reciprocating tray, an example of which is disclosed in Korean Patent Laid-Open No. 2005-12410, is under development.
The disclosed tray assembly is constructed such that an oval recess, i.e. a kind of rail, is formed on the bottom surface of a first tray, a first cam shaft rotated by a motor moves along the first recess, and the first tray linearly reciprocates. However, in the disclosed conventional tray assembly, since the first recess is configured to allow the first tray to swing from the left side to the right side, time when the first tray travels through the central area of a cooking chamber is longer than time when the first tray stays at the left or right side of the cooking chamber. Thus, since food is mostly cooked at the central area of the cooking chamber, food cannot be uniformly cooked.
Moreover, according to the conventional tray assembly, since the first camshaft inserted into the first recess travels along the first recess to move the first tray, the first camshaft tends to easily escape from the first recess unless the first recess is formed at a sufficient depth. In the conventional tray assembly, since an accommodating part for accommodating a second tray must be formed above the first tray and the first recess must be formed in the bottom surface of the first tray, there is a limit to the depth of the first recess.
Additionally, in the conventional tray assembly, since the first camshaft and a second camshaft are respectively inserted into the first recess of the first tray and a second recess of the second tray, the tray assembly is not easily assembled. Thus, the conventional tray assembly is inconvenient for a user to clean the bottom of the cooking chamber and to install the conventional tray assembly.